Computer printer technology has evolved to a point where very high-resolution images can be transferred to various types of media, including paper. Ink-jet printing involves the placement of small drops of a fluid ink onto a media surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. Within this general technique, the specific method that the ink-jet ink is deposited onto the printing surface varies from system to system, and can include continuous ink deposit and drop-on-demand ink deposit. Regarding drop-on-demand printing systems, the ink-jet inks are typically based upon water and solvents such as glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave such that all of the ink droplets ejected are used to form the printed image.
There are several reasons that ink-jet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, capability of high-speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers. With respect to ink-jet ink chemistry, the majority of commercial ink-jet inks are water-based. Thus, their constituents are generally water-soluble, as in the case with many dyes, or water dispersible, as in the case with pigments. Furthermore, ink-jet inks have low viscosity to accommodate high frequency jetting and firing chamber refill processes common to ink-jet architecture.
Traditionally, dyes have been used as colorants in thermal ink-jet inks due to their vibrant colors, low cost, and compatibility with thermal ink-jet pens. However, images produced by dye-based inks tend to lack durability, i.e., they exhibit low water fastness, smear fastness, and light fastness. Replacing dyes with pigments as colorants can improve some of these properties, but the presence of pigments can result in images that have a surface that can suffer from lessened smear fastness. Polymers may be used in ink-jet inks to improve image durability. When present as additives, polymers can contribute to increased viscosity due to the increased number of particles suspended in the ink. Conversely, pigments may be encapsulated in polymers, thereby providing the desired durability benefits with fewer particles per unit volume. However, many pigment particles present functional groups that inhibit polymerization, resulting in incomplete encapsulation and the presence of appreciable amounts of residual monomers in the resulting suspension. Therefore, ink-jet applications would benefit from pigment-based ink-jet inks that feature pigments with improved encapsulation.